## **Core Concept**
Nephrotic syndrome is a collection of clinical findings due to kidney damage, characterized by severe proteinuria (>3.5 g/1.73 m²/day or >40 mg/m²/hr), hypoalbuminemia, hyperlipidemia, and edema. In children, the most common cause is minimal change disease (MCD), which accounts for about 80% of cases.

## **Why the Correct Answer is Right**
- **a) Minimal change disease is commonest cause**: This statement is correct. Minimal change disease is indeed the most common cause of nephrotic syndrome in children, accounting for approximately 80% of cases. It is characterized by the loss of foot processes of the podocytes and typically responds well to corticosteroid therapy.
- **b) Proteinuria of 4 gm/m2 hr is characteristic**: While significant proteinuria is a hallmark of nephrotic syndrome, the characteristic feature is proteinuria >40 mg/m²/hr or >3.5 g/1.73 m²/day. The specific value of 4 gm/m²/hr might not universally define nephrotic syndrome but indicates significant protein loss.
- **c) Cyclosporine & Azathioprine is mainstay of therapy**: The initial mainstay of therapy for minimal change disease, the most common cause of nephrotic syndrome in children, is corticosteroids, not Cyclosporine or Azathioprine. However, these drugs are used in cases of steroid dependence or resistance.
- **d) Pretreatment biopsy is done in all cases**: This statement is not correct. In children, a pretreatment biopsy is not routinely done for nephrotic syndrome if the presentation is typical for minimal change disease and there is a good response to corticosteroids. Biopsy is considered in atypical cases or if there's no response to initial therapy.
- **e) Spontaneous bacterial peritonitis is associated with it**: This statement is correct. Spontaneous bacterial peritonitis (SBP) is a complication associated with nephrotic syndrome, particularly in patients with cirrhosis and ascites, but it can also occur in patients with nephrotic syndrome.

## **Why Each Wrong Option is Incorrect**
- **Option C:** This option suggests that Cyclosporine & Azathioprine are the mainstay of therapy, which is not accurate for initial treatment but can be used in specific scenarios.
- **Option D:** Pretreatment biopsy is not done in all cases; it's reserved for atypical presentations or failure to respond to corticosteroids.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **minimal change disease** is the most common cause of nephrotic syndrome in children and typically has a good response to **corticosteroids**. Another important point is that **spontaneous bacterial peritonitis** can complicate nephrotic syndrome.

## **Correct Answer: A.**